Many types of semiconductor devices are made using similar manufacturing procedures. A starting substrate, usually a thin wafer of silicon, is doped, masked, and etched through several process steps, the steps depending on the type of devices being manufactured. This process yields a number of semiconductor devices (dies) on each wafer produced. Each die on the wafer is given a brief test for functionality, and the nonfunctional devices are mechanically marked or mapped in software. This probe test is only a gross measure of functionality, and does not insure that a device is completely functional or has specifications that would warrant its assembly in a package.
If the wafer has a yield of grossly functional devices which indicates that a significant number of devices from the wafer are likely to be fully operative, the devices are separated with a die saw (diced) into discrete devices, and the nonfunctional devices are scrapped while the functioning devices are individually encapsulated in plastic packages or mounted in ceramic packages with one device in each package. After the diced devices are packaged they are rigorously electrically tested. Components which become nonfunctional or which operate below full industry specifications are scrapped or devoted to special uses.
Packaging unusable devices only to scrap them after testing is costly. Given the relatively low profit margins of commodity semiconductor components such as dynamic random access memories (DRAMs) and static random access memories (SRAMs), this practice is uneconomical. However, no thorough, cost effective, and automated method of testing an unpackaged device is available which would prevent this unnecessary packaging of nonfunctional and marginally functional devices.
It is becoming more common to package multiple integrated circuit devices as a single unit, known as a multi chip module (MCM). Testing of each device before it is assembled into the MCM is difficult because the conventional lead frame package is not typically used for the manufacture of MCMs. The reliability of the entire package is compromised by the individual component with the least performance capability. Although there is no industry standard by which devices are tested and considered "known good die," it is desirable to have the ability to retest the individual die being used on a particular MCM to increase the potential for greater yields. The ability to presort an individual device is limited to results obtained through probe testing, which is only a gross measure of functionality and does not typically result in information regarding access times or reliability. An MCM is burned in after assembly, which can result in the failure of one or more DRAMs. If a single device is nonfunctional or operates outside of acceptable specifications, the entire component fails and all devices in the package are scrapped or an attempt is made to "re-work" the MCM. There is presently no cost-effective way to reclaim the functioning devices.
Statistically, the yields of MCMs decrease in proportion to the increasing number of devices in each module. The highest density modules have the lowest yields due to their increased total silicon surface area. Testing of unpackaged devices before packaging would be desirable as it would result in reduced material waste, increased profits, and increased throughput. Using only known good devices in multichip modules would increase yields significantly. An apparatus which allows for the handling and testing of an unpackaged semiconductor device would be desirable. Similarly, an apparatus which would allow a user of diced devices purchased from a manufacturer to test incoming devices would be desirable.